Start with your colors. The colors make the theme. Specify them in the "Colors" tab. To see which colors a website of your customer uses, open the console of your browser and select the element with the preferred color. Alternatively, for chrome use the "eye dropper color picker" plugin. However please note colors selected by the color picker might be a slightly bit different from the original. The color picker is especially handy when selecting colors from images, rather than HTML elements.
To use different fonts, you need to import them in the less or scss config. For bootstrap 3, you can edit the theme.less by clicking the "Edit theme.less"-button. For bootstrap 4 fonts should be imported in the custom.scss. Here you can import fonts via URL in this way:
After doing this you can use the font throughout your bootstrap theme. Selecting the font as base font can be done in the "Typography" tab of your theme builder.
Download at least the unminimized css file. This is the readable version of your css and it can be loaded in molgenis using the theme manager. If you created a theme for a specific project, put it in the molgenis-projects repository on github. Downloading the .less files for bootstrap 3 and the .scss files for bootstrap 4 and uploading them later again enables for continuing on your styling in the theme builder in future.
Making bootstrap 3 and 4 themes look the same
There is not a real trick for this. Throughout the application the classes between bootstrap 3 and 4 are not always consistent. There are however always some steps that need to be done to accomplish this.
1. Determine which font-size you want to use.
Bootstrap 3 uses 14px as basic font size whereas bootstrap 4 uses 16 px. To change the default of bootstrap 3 to 16px, set the @font-size-base to 16px in the "Typography" section. To change the default of bootstrap 4 to 14px, set the $font-size-base of the "Typography" section to 0.875rem.
2. Set the same colors
Set your own colors, or copy either the colors of bootstrap 3 of bootstrap 4 to both themes in the "Color" section. Bootstrap 4 has an additional secondary color, which is not in bootstrap 3, here you can use the info color, or another if you prefer.
3. The menu
To make the menu look the same, use your browsers debugger to compare the bootstrap 3 and 4 theme and copy css styling between the two until they look the same. Do the same alterations in your bootstrap css. Some of the alterations you want to do cannot be done in the theme builders. Paste this css code well documented on top of you bootstrap theme file. Be careful with the !important.
4. Sign in and sign out button
These buttons have such different classes between the bootstrap 3 and 4 molgenis menu, that you probably don't want to focus too much on them.