How to customize color and font size

Hello Mostofa ! 
To change the font size of title on widget like News Slider, Popular News, Category widget, you can log in to Dashboard > Appearance > Customize > General Setting, add the following code to the Header Code: 

 <style>
.news-slider .carousel .carousel-inner .entry-title {
 font-size: 20px;
}
.news-slider .carousel-list .other-entry h2 {
 font-size: 14px;
}
.home #primary .widget .tab-pane .entry-title {
 font-size: 15px;
}
.widget.news-category article .entry-title {
 font-size: 16px;
}
.widget .entry-title {
 font-size: 21px;
}
#secondary .widget.latest-news .hentry.first .entry-title {
 font-size: 16px;
}
</style>

– To change font-size & color for the headline scroll in the DW Focus, you can add the following code to the Header Code:

 <style>
#under-navigation .dw_focus_headlines .widget-title {
    color: #...;
    font-size: 11px;
}
#under-navigation .dw_focus_headlines .headlines a {
    color: #...;
    font-size: 11px;
}
#under-navigation .dw_focus_headlines .headlines a:hover {
   color: #...;
}
#under-navigation .dw_focus_headlines .headlines ul {
    color: #...;
}
</style>

Hope this helps !

Hi Mostofa !
Please add the following code to the Header Code:

 <style>
#secondary .widget .widget-title {
   font-size: 11px;
   color: #...;
}

.accordion .accordion-heading a {
   font-size: 11px;
   color: #...;
}
.nav-tabs a {
   font-size: 11px;
   color: #...;
}
.news-slider .carousel-list h3{
   font-size: 11px;
   color: #...;
}
</style>

Hope this helps !