Fix W3C CSS validation issues

Problem/Motivation

The following issues were reported after using https://jigsaw.w3.org/css-validator/ on a project that uses a Vartheme subtheme:

#admin-menu-search .form-control	Value Error : float auto is not a float value : auto
.form-required::after	Value Error : width Too many values or values are not recognized : calc(1.445em + 1.376rem + 4px) / 2
.form-required::after	Value Error : height Too many values or values are not recognized : calc(1.445em + 1.376rem + 4px) / 2
.form-required::after	/ is not a background-size value : calc(1.445em + 1.376rem + 4px) / 2 calc(1.445em + 1.376rem + 4px) / 2
.form-required::after	Value Error : width Too many values or values are not recognized : calc(1.445em + 1.376rem + 4px) / 2
.form-required::after	Value Error : height Too many values or values are not recognized : calc(1.445em + 1.376rem + 4px) / 2
.form-required::after	/ is not a background-size value : calc(1.445em + 1.376rem + 4px) / 2 calc(1.445em + 1.376rem + 4px) / 2

Proposed resolution

Change the factor to 6

    background-size: calc(#{$input-height} / 6) calc(#{$input-height} / 6);
    width: calc(#{$input-height} / 6);
    height: calc(#{$input-height} / 6);

User interface changes

After the Fix

API changes

• None

Data model changes

• None